NATURAL SCIENCES OF PHILADELPHIA. 211 



■with three or four serrations near the extremity; three opposite 

 the dorsal fin much elevated, two in front of them small, spine- 

 less. Radii D. I. 6; C. -f 17 + ; A. 11 ; Y. t; P. I. 8. Dorsal 

 spine very strong compressed, with teeth pointing downwards 

 behind and upwards before ; its length one-half length of fish an- 

 terior to it. Pectoral spine flat, striate, with strong teeth on 

 both faces, the posterior the longer. Bye looking partly upwards, 

 covered with rather thick cornea 8.5 times in length to bony oper- 

 cular margin, a little less than half interorbital width. Muzzle 

 flattened and narrowed, the maxillary beards leading to the mid- 

 dle of the humeral process, the mental beards half as long. 

 Rugosity of the casque striate, bifurcating at the fontanelle, and 

 sending an angle to the front of each orbit, and then ceasing. A 

 weak serration of the small preorbital bone visible. Head flat 

 between the orbits, the casque steeply roof-shaped, contracting 

 and then expanding downwards opposite the dorsal spine, but 

 not exceeding it. Humeral spine extending to opposite dorsal ; 

 flat, striate; postcoracoid short, covered with smooth skin. Ven- 

 tral fin commencing some distance behind last dorsal ray, obtuse, 

 not reaching vent, but reached b}'- the pectoral spine. Caudal 

 peduncle short; caudal fin deeply furcate. Adipose fin well de- 

 veloped, but low. Teeth numerous, brush-like. 



Total length .382 m. Length to e^-e .031; to dorsal spine .12 ; 

 to ventral fin .165; to anal fin .222; to basis of caudal fin .31. 

 Width at humeral swellings .017 ; height at basis D. I. .095. 



Colors bright ; above brownish, sides pink, below white. Fins 

 red, except pectoral and dorsal, which are paler. 



This marked species is very different in general physiognomy 

 and details from such short, rough, black species as D.pectinifrona 

 and D. grypiis, being elongate in form, and smooth, though well 

 armed. Discovered by Robert Perkins between the mouth of the 

 Rio Negro and the Huallaga, in the Marauou. 



ZATHOKAX, Cope, gen. nov. 



Proc. Acad. N. Sci. Pliila., 1871, p. 112. 



Branchial fissure much contracted. Lateral shields not meet- 

 ing on the middle line of the back. No adipose fin? dorsal and 

 anal fins short. Spines and postclavicular process strong. Ven- 

 trals behind dorsal. Scapular arch dilated below and covered 

 with a dermo-ossification. 

 1872.] 



